Fuel cell power systems have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One type of fuel cell power system employs use of a proton exchange membrane (PEM) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as air or oxygen) into electricity. Typically, the fuel cell power system has more than one fuel cell that includes an anode and a cathode with the PEM therebetween. The anode receives the hydrogen gas and the cathode receives the oxygen. The hydrogen gas is ionized in the anode to generate free hydrogen ions and electrons. The hydrogen ions pass through the electrolyte to the cathode. The hydrogen ions react with the oxygen and the electrons in the cathode to generate water as a by-product. The electrons from the anode cannot pass through the PEM, and are instead directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle. Many fuels cells are combined in a fuel cell stack to generate the desired power.
The fuel cell power system can include a processor that converts a liquid fuel, such as alcohols (methanol or ethanol), hydrocarbons (gasoline), and/or mixtures thereof, such as blends of ethanol/methanol and gasoline, to the hydrogen gas for the fuel cell stack. Such liquid fuels are easy to store on the vehicle. Further, there is a nationwide infrastructure for supplying the liquid fuels. Gaseous hydrocarbons, such as methane, propane, natural gas, LPG, etc., are also suitable fuels for both vehicle and non-vehicle fuel cell applications. Various reformers or processors are known in the art for converting the liquid fuel to gaseous hydrogen suitable for the fuel cell.
Alternatively, the hydrogen gas can be processed separate from the vehicle and stored at a filling stations and the like. The hydrogen gas is transferred from the filling station to a high pressure vessel or container on the vehicle to supply the desired hydrogen gas to the fuel cell engine as needed. The high pressure vessels are typically classified into one of four types: a Type I vessel having an all-metal construction; a Type II having a metal lined construction with a fiberglass hoop wrap; a Type III having a metal lined construction with a composite full wrap; and a Type IV having a plastic lined construction with a composite full wrap.
High pressure vessels containing a compressed hydrogen gas must have a mechanical stability and an integrity that militates against a rupture or bursting of the pressure vessel from the pressure within. It is also typically desirable to make the pressure vessels on vehicles lightweight so as not to significantly affect the weight requirements of the vehicle. The current trend in the industry is to employ the Type IV pressure vessel for storing the compressed hydrogen gas on the vehicle.
As is reported by Immel in U.S. Pat. No. 6,742,554, herein incorporated by reference in its entirety, the Type IV pressure vessel contemplated in the industry for storage of hydrogen gas is cylindrical in shape to provide the desired integrity, and includes an outer structural wall and an inner liner defining a container chamber therein. The combination of the outer wall and the liner provide the desired structural integrity, pressure containment, and gas tightness in a light-weight and cost effective manner.
The Type IV pressure vessel typically includes an adapter that provides the inlet and outlet opening for the hydrogen gas contained therein. The adapter typically houses the various valves, pressure regulators, piping connectors, excess flow limiter, etc. that allow the pressure vessel to be filled with the compressed hydrogen gas, and allow the compressed gas to be discharged from the pressure vessel at or near ambient pressure, or a higher pressure, to be sent to the fuel cell engine. The adapter is generally made of steel to provide a desired structural strength for storing compressed hydrogen gas. A suitable adhesive, sealing ring, or the like is employed to seal the liner to the adapter in a gas tight manner, and secure the adapter to the outer wall.
High pressure vessels are also generally designed with a thermally activated safety valve or pressure relief device (PRD), typically located at the adapter or opening of the pressure vessel. A PRD is a necessary component for a variety of safety reasons, including situations involving accidental damage to the fuel cell power system and the potential for resulting high temperatures or fire. The use of more than one PRD is desirable, in particular where high temperatures might occur at a side opposite the PRD in conventional pressure vessels. However, having more than one PRD has required an expensive construction that includes the drilling of an additional liner opening for placement of a second adapter and PRD. This drilling operation generally must occur during the final stages of a vessel manufacturing process and must be very precise in order to maintain the vessel integrity. A risk of irreparably damaging the vessel at these stages is also significant.
There is a continuing need for a high pressure vessel for the storage of hydrogen having a second pressure relief device for improved safety. Desirably, the pressure vessel also is constructed without significantly affecting the complexity of the vessel construction.